Upgrading libhybris

One of the most important dependencies for our phone project is libhybris. Libhybris is a neat technology to allow interfacing with Android drivers allowing for example to bring Wayland to a device where all we have are Android drivers.

Given that KWin provides a hwcomposer backend which uses libhybris to create an OpenGL context. All other applications need libhybris indirectly to have the Wayland OpenGL buffer exchange work automatically.

When we started the work on the hwcomposer backend we based it on the libhybris version used in Ubuntu (0.1.0+git20131207) as we used Ubuntu as the reference platform. Soon enough we noticed that this version diverged a lot from the upstream version. Lots of recent changes are missing and there are API incompatible changes.

This made working with it difficult. How much time should we invest in investigating issues? Should we write code which we know might break once Ubuntu decides to upgrade libhybris? How well is Wayland integrated in the Ubuntu version given that they don’t need it? If we need help, who to talk to? Ubuntu who will tell us that they don’t know anything about Wayland, or the libhybris devs who might just tell us: use later version?

Furthermore we want other distributions to provide Plasma for the phone. This means they need to provide libhybris. Of course this is difficult if we need to tell them that we need exactly the version used by Ubuntu. And even more it might conflict with other uses. Considering distributions like Mer would have to chose between a libhybris for Plasma and a libhybris for lipstick.

With that in mind we wanted to invest some time on upgrading libhybris in our stack in this release cycle and then fix the issues we were seeing in the stack. Our awesome packagers did the job of creating packages so that I can port KWin against it. And in deed after some hacking I had KWin rendering again. A more difficult task was to get other applications to work as we run into a problem that libwayland-egl does not use the alternatives system. Thus our packagers needed to do some ld tricks to get this worked around. But with that we had a nice rendering system.

A surprise in this exercise was that our input handling code in the hwcomposer backend didn’t compile any more. The code was gone. While that was in the first moment an unpleasant surprise, it soon turned into something wonderful. If that code is not needed at all on an Android powered device it means that we must be able to get libinput to work with it. 400 lines of code deleted and it’s using the shared input stack through libinput. I’m very happy about that!

With that all in place we finally were able to investigate the rendering issues we were seeing. My hope was that just upgrading libhybris would fix the visual tearing, but unfortunately not. While I’m still surprised that it’s possible to get tearing in the first place on Android devices (hey ever heard of things like Atomic Mode Settings, Android?), it at least gives us a vsync event. Unfortunately the only tear-free solution I could find invokes blocking till we get the event. I don’t like that and I think that’s a bad architecture. One can have blocking free and tear free rendering. Our DRM (kernel mode setting) backend can do so with an easy to use API. Really disappointing that the Android stack is in that regard not better than the glx backend. But well at least it’s tear free 🙂

As we now use upstream libhybris I hope to see distributions to pick up the work and provide a Plasma phone spin. I’d love to see an openSUSE phone or a Fedora phone (or any other distribution). Distributions: you can of course ask us on how to integrate 🙂